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(11) | EP 0 067 020 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Hydrostripping process of crude oil |
| (57) Hydrostripping process which is the combination of crude oil distillation and hydrotreating
of distillate overhead wherein crude oil is distilled with hydrogen rich gas at high
temperature and under high pressure. Hydrogen partial pressure at the distilled vapor phase in a stripper (4) which is enough for a desulfurization reaction is maintained sufficiently to allow a smooth distillation processing whereby an efficient crude oil stripping performed. The distillate overhead thus produced is maintained at a temperature high enough for direct feeding to a subsequent hydrotreating process by means of a reflux cooler (6) installed at the top of the stripper (4), thereby eliminating any intermediate process such as an adjusting process. |
[0001] This invention relates to a refinery system, more particularly, it is concerned with a hydroskimming process for hydrodesulfurization of distillate overhead from the top of a crude oil stripper wherein crude oil mixed with a large amount of hydrogen is seperated into distillate overhead and heavy residue at high temperature and pressure.
[0002] It is a recent tendency that almost all distillates have been desulfurized under high hydrogen partial pressure, to extend the life of the catalysts for as long as possible and to prevent any worsening of environmental contamination. Therefore, the hydrogen requirements and the adoption of hydroskimming refinery system have been increasing every year.
[0003] The situation mentioned above and a concern for energy conservation at refineries are creating the motives for making further research and developments for new hydrogen processing and crude oil separation techniques. This tendency may be accelerated by the use of sour crude oil as feedstock.
[0004] There are a couple of newly developed processes which is known in accordance with the prior art described in a Japanese patent No. 823438 and a Japanese patent provisional publication No. 1979-20007. The former is concerned with a crude separation system by which crude oil mixed with hydrogen at high temperature and high pressure is separated into two fractions such as distillate overhead and residue.. The separated overhead is sent to a subsequent process designed for an overhead distillate hydrodesulfurization reaction, while the residue is pumped to an operating pressure necessary for residue hydrodesulfurization before being mixed with a large excess of hydrogen and introduced into a heater.
[0005] The latter is also concerned with a crude separation process by which crude oil is distilled with hydrogen rich gas at a temperature between 350°C and 500°C and at a pressure between 10 kg/cm2G, and 100 kg/cm2G, whereby the crude oil is separated into various fractions ranging from light naphtha to VGO equivalents.
[0006] However, when the stripped lighter fraction such as distillate overhead is introduced to a subsequent hydrodesulfurization process, it is necessary for the lighter fraction to be reheated to the temperature required for an efficient processing before its introduction thereto by means of additional devices such as a start-up heater and heat exchangers, which usually brings further complexities to the operation of.the system.
[0007] The invention as claimed is intended to provide a most efficient and economical hydrodesulfurization process of crude oil by the combination of hydrogen stripping and hydrotreating system wherein disengaged distillate overhead may be introduced directly to a subsequent device such* as a hydro-desulfurization reactor without any heat adjustment process being employed after the overhead is withdrawn from the hydrogen stripping device to be fed to the subsequent hydrotreating process. The combination of hydrogen stripping and hydrotreating system as heretofore explained is hereinafter called hydrostripping process.
[0008] The invention is also intended to provide an economical process by obtaining the temperature, the pressure and the ratio of hydrogen to oil available for an efficient operation of the hydrostripping system.
[0010] Crude oil after being desalted and filtered is pumped to a pressure between 50 kg/cm2G and 70 kg/cm2G and is mixed with hydrogen rich gas in an amount ranging from 50 Nm3 and 200 Nm3 (as pure H2) per m3 of crude. Crude mixed with hydrogen is introduced to a crude oil heater wherein the mixture is heated to a temperature between 360°C and 430°C before sending to a stripper at the bottom of which is charged continuously an additional hydrogen rich gas which is heated to a temperature between 350°C and 550°C in an amount ranging from 50 Nm3 to 200 Nm3 (as pure H2) per m3 of crude. In the stripper the mixture of crude and hydrogen rich gas thus produced is distilled and disengaged into two fractions, gas oil and lighter fractions and a heavier residue fraction.
[0011] A reflux cooler installed at the stripper top helps separate crude oil into two fractions as explained heretofore and also prevents the contamination of heavier residue from carrying over to a subsequent gas oil and lighter hydrodesulfurization process and at the same time maintains the temperature of distillate overhead higher than that of start run condition of the subsequent hydro- desulfurizing reaction, said temperature being maintained, for example, between 340°C and 385°C.
[0012] Naturally the gas oil and lighter fraction produced in the stripper can be fed directly to the subsequent process for desulfurization without any temperature adjustment process being employed therebetween, thereby a continuous and efficient operation of the process is achieved, while the heavier residue can be fed to a buffer tank and onto another hydrodesulfurization process etc., as in conventional flow patterns.
[0013] The advantage of this invention which is the combination of crude oil distillation and hydrotreating process for the distillate overhead is obtained by an effective use of high temperature latent heat generated at the top of the stripper and integration of the heat and energy for the distillation and hydrotreating units without consuming steam as used in a conventional topping unit or vacuum unit.
[0014] preferred A. L feature of this invention is to obtain distillate overhead whose temperature is maintained higher than that of the run condition of a subsequent hydrodesulfurization reaction under high pressure ranging from 40 kg/cm2G to 60 kg/cm2G, middle distillates and lighter fractions obtained thereby boiling in the IBP-525°C range, preferably in the IBP-340oC range. The advantage and feature stated above have never been accomplished by any prior art.
[0015] The refiners recently attempted deep distillation in the topping unit to gain more lighter fractions from crude oil, moved deeper into the barrel and installed a separate hydrotreating plants of higher pressure design to take sulfur out of even vacuum gas oil in order to improve catalytic cracking plant performance or to hydro crack directly to gasoline and fet fuels. The deep distillation of this type can also be performed by the hydrostripping process of this invention. It should be noted, however, that the purpose of this invention is not to provide a method of cracking crude oil even if cracking may slightly occur at the said temperature range.
[0016] One way of carrying out the invention is described in detail below with reference to drawings which illustrate only one specific embodiment, in which: Figure 1 indicates a schematic flow chart for the practice of the present invention, Figure 2 shows graphically the yeild of distillate overhead gas oil and residue obtainable by the process of the present invention.
[0017] Referring to Figure 1, crude oil from line (1) is elevated to a pressure, for example 60 kg/cm2G, after being desalted and filtered and is mixed with a large excess of hydrogen supplied from line (2) by means of a recycle compressor (12) in an amount 106 Nm3 (as pure H2) per m3 of crude oil. The mixture is then introduced into a crude oil heater (3) and after being heated to a temperature of 388°C therethrough is fed to a crude oil stripper (4) equipped with 9 trays wherein a high temperature and a high pressure are maintained.
[0018] Additional hydrogen for stripping in an amount 106 Nm3 (as pure H2) per m3 of crude is charged at the bottom of said stripper (4) through line (5), wherein the mixture of crude and the hydrogen thus processed is separated and distilled into two fractions.
[0019] A distillate overhead, one of the fractions, after being cooled by a reflux (7) generated by and circulated through a reflux cooler (6) installed at the top of the stripper (4), is fed directly to a subsequent hydrodesulfurization reactor (10) for processing through line (8) and then introduced to a fractionator (11).
[0020] The reflux (7) generated by and circulated through the reflux cooler (6) installed at the top of the stripper (4)also helps disengage the crude into overhead and residue. The bottom residue collected at the stripper bottom may be sent to the hydro- desulfurization unit and/or hydrocracker unit through a buffer- tank (not shown) by line (9).
[0021] The yield shown in Figure 2 is obtainable when Khafji crude (28.4° API and 2.85 wt%S) is used as a charged stock in the following manner.
[0022] Khafji crude from line (1) is pumped to a pressure of about 60 kg/cm2G and after being desalted and mixed with hydrogen rich gas composed of 80 vol% H2, 75 vol% C1 and 3 vol% C2 in an amount of 106 Nm3 (as pure H2) per m3 of crude, and after being heated to a temperature of 388°C through the heater (3), is sent to the crude oil stripper (4). Additional hydrogen rich gas of the same composition and ratio to crude as mixed with Khafji crude is charged at the bottom of stripper (4) through line (5), wherein the mixture of crude and hydrogen thus prepared is separated into two fractions, as shown in Figure 2, at the pressure of 44 kg/cm2G and at the temperature of 343°C measured at the top of the stripper (4). Hydrogen partial pressure in distilled vapor phase is about 30 kg/cm2 at 343°C which is high enough for desulfurization reaction.
1. A process for hydrodesulfurization of distillate overhead sent from the top of
a crude oil stripper wherein crude oil mixed with a large amount of hydrogen is separated
into said distillate overhead and heavy residue at high temperature and pressure,
characterized in that a reflux cooler installed at the top of the stripper/not only
promotes distillation of crude oil but also adjusts the temperature of said distillate
overhead by maintaining it higher than that of the start of run condition of a subsequent
hydrodesulfurization reaction for distillate overhead, whereby the direct supply of
said overhead into the hydrodesulfurization reactor (10) can be performed, such that
a continuous and efficient operation of the process may be achieved.
2. The process as claimed in claim 1, wherein distillate overhead boiling in the ranges
between IBP-340°C and IBP-525°C is provided from the top of the crude oil stripper
(4) to which crude oil mixed with hydrogen rich gas in an amount ranging from 50 Nm3
to 200 Nm3 (as pure H2) per m3 of crude is introduced and mixed therein with additional hydrogen rich gas
of the same amount as mixed with said crude, which is charged at the bottom of said
stripper, said mixture of crude and hydrogen rich gas being separated therein into
said distillate overhead and heavier residue at a pressure between 40 kg/cm2G and 60 kg/cm2G, while hydrocarbons reflux from the reflux cooler (6) at said stripper top promoting
the performance of the distillation process.
3. The process as claimed in claim 2, wherein crude mixed with hydrogen rich gas is
heated to a temperature between 360°C and 430°C at the crude heater (3) before being
fed. to the crude oil stripper (4).
4. The process as claimed in claim 2, wherein the hydrogen rich gas heated to a temperature
between 350°C and 550°C is charged at the bottom of the crude oil stripper (4).